1. Technical Field
The present invention relates to input devices in general, and particularly to a thin keyboard that locates each key in a ready position by means of magnets.
2. Description of Related Art
A keyboard is supposed to give a user an operation feeling (tactile) of a switching operation with a finger and not to give the user a feeling of fatigue even when the user performs keyboard operations for a long time. To accommodate the needs, a so-called pantograph type keyboard is employed in many laptop personal computers (laptop PCs). In the pantograph type keyboard, each key includes a supporting structure called a pantograph (or a scissor mechanism) and an elastic member called a rubber dome to give a reaction force to the pressing pressure of a finger.
The pantograph type keyboard is so configured that as a depressed keycap travels in a vertical direction little by little, the bottom of the pantograph gradually crushes the top of the rubber dome. As the travel distance in the vertical direction gets longer, the degree of deformation of the rubber dome gets larger, increasing the reaction force to the finger. Then, when the travel distance becomes further longer, the top of the rubber dome that has just reached a yield point gets dented suddenly, resulting in a drop in reaction force.
Since the key switch is set to operate immediately after the yield point, the user feels the drop in reaction force and becomes aware of the operation of the key switch. Since the user cannot stop the operation of the finger suddenly even if the user feels a sudden drop in reaction force, the user further holds the key down even after the key switch is activated. After the reaction force is further increased along with traveling of the key, the user eventually stops the pressing operation. Such an operation feeling cannot be derived from a software keyboard appearing on a display. The operation feeling is a characteristic unique to a keyboard involving physical traveling of a key.
Since the pantograph can maintain the posture of a keycap even if an edge of the keycap is pressed down with a finger, the top face of the keycap is maintained substantially in a horizontal position while the keycap is traveling in the vertical direction. However, a predetermined stroke is required for traveling of the keycap in the vertical direction, the pantograph type keyboard has a limitation on the application to thin laptop PCs.
FIG. 15 is a side cross-sectional view for describing the principle of a thin keyboard that gives an operation feeling as approximate as that given by a pantograph type keyboard. A key 10 includes a keycap 11, a frame 19, and a base 21. A magnet 17b is mounted in an edge portion of the keycap 11, and a magnet 17a for attracting the magnet 17b is mounted in the frame 19. Chamfers 13a and 13b are formed on the lower side (inner side) of the keycap 11.
Ramps 15a and 15b each having a chamfer are provided on the base 21. The shapes and angles of the chamfers 13a and 13b are adjusted to slide on the chamfers of the ramps 15a and 15b. Only two pairs of chamfers and ramps are shown in the figure, but they are actually placed below the four corners of the keycap 11 whose flat surface is shaped into a rectangle. FIG. 15A shows a ready position before the key 10 is pressed down. In the ready position, the keycap 11 is located at the topmost position in a Z-axis direction (vertical direction) by a magnetic attraction between the magnets 17a and 17b. At this time, four sets of ramps and chamfers maintain the keycap in a horizontal position.
FIG. 15B shows a state in which the key 10 is pressed down. In the ready position, since the magnets 17a and 17b are strongly attracted to each other, the finger is made to feel resistance to the pressing force. When the pressing force is increased to overcome the resistance, the chamfers 13a and 13b slide down the chamfers of the ramps 15a and 15b to generate a force component in the X-axis direction (horizontal direction) against the pressing force in the Z-axis direction. Thus, when the key 10 is pressed down, the keycap 11 travels in the Z-axis direction and the X-axis direction at the same time.
The magnetic attraction between the magnet 17a and the magnet 17b is inversely proportional to the square of the distance. When the magnets are separated by a certain distance or more, the magnetic attraction between both magnets and the resistance to the finger caused by the magnetic attraction drop suddenly, shifting to a state shown in FIG. 15C. In FIG. 15C, the keycap 11 travels to the maximum position limit in the Z-axis direction and the X-axis direction to activate the key switch (not shown) placed on the surface of the base 21. At this time, the user feels a sudden drop in resistance to the finger and becomes aware of the operation of the key switch.
When the user lifts the finger off the key or weakens the depression force, the keycap 11 is returned to the ready position by the magnetic attraction between the magnets 17a and 17b. The sets of chamfers of the keytop and chamfers of the ramps maintain the posture of the keycap 11 during the ready position and traveling. The keycap 11 travels in the Z-axis direction by a predetermined stroke, but the user feels as if the keycap 11 traveled by a stroke longer than the predetermined stroke until the user feels a strong reaction force to the finger. Thus, the key 10 can convert the depression pressure on the keycap 11 into traveling in the vertical direction and the horizontal direction not only to give a good operation feeling while keeping the keycap 11 in a horizontal position, but also to make the keyboard thinner.
The keyboards disclosed in the related art documents include a mechanism for converting the depression pressure in the vertical direction into traveling of the key in the vertical direction and the horizontal direction. Hereinafter, this type of keyboard is called an oblique slide-type keyboard in this specification. The oblique slide-type keyboard is so configured that the surface of the keycap 11 in the ready position is protruded by a length S from the surface of the frame 19 as shown in FIG. 15A.
When the oblique slide-type keyboard is mounted on a laptop PC, it is necessary to have a clearance between a display and the keyboard face to protect keycaps or the display from being damaged when a display housing is so closed that the display and the keyboard face each other. Since the length of the keyboard in the vertical direction in FIG. 15A becomes one of factors for deciding on the thickness of the laptop PC, it is desirable to make the oblique slide-type keyboard even thinner.